(a) Field of the Invention
This invention relates to fluid milk in which a major amount of the lactose present therein has been hydrolyzed by lactase enzymes and to milk products derived therefrom and more specifically to such fluid milk and milk products which incorporate potassium chloride to counteract increased sweetness resulting from lactose hydrolysis.
(b) Information Disclosure Statement
It is generally known that milk and milk products contain high percentages of lactose. For example, the lactose content of regular homogenized pasteurized milk (3.5% butterfat) is 4.9%, of lowfat milk (2% butterfat) is 6.0%, and of fluid skim milk is 5.1%.
It is well known to those familiar with the state-of-the-art, that there exists a significant population which cannot totally digest lactose. This population is generally referred to in the professional literature as lactose intolerant. The estimated number of individuals exhibiting lactose malabsorption in the USA is between 28 and 75 million. The incidence in certain population sub-groups is significantly higher than others. For example, it is estimated that lactose intolerance in American blacks may be over 60%, whereas the incidence in American whites is less than 25%.
It is generally believed that individuals suffering from lactose intolerance have lactase deficiency. Several approaches have been undertaken by the industry to alleviate this problem. Generally, these approaches may be classified into two categories:
(1) Providing to the lactose intolerant individual an enzyme preparation which contains a stabilized form of lactase. This preparation is ingested within a prescribed time prior to or with the ingestion of the lactose containing products. PA1 (2) Hydrolyzing the lactose using lactase enzymes prior to its ingestion. For example, lactase enzymes are added to fluid milk and sufficient time is allowed to assure the hydrolysis of the lactose into glucose and galactose.
Lactase is a trivial name for the .beta.-galactosidases which catalyze the hydrolysis of lactose to its component saccharides, glucose and galactose. Sources of lactase, including commercial sources, are described in the literature. See, for example, R. R. Mahoney, Developments In Dairy Chemistry, Chapter 3, Edited by P. F. Fox, Elsevier Applied Science Publishers, 1985. Lactase enzymes used in processing dairy foods are derived from the yeasts Kluyveromyces fragilis, Kluyveromyces lactis and Clandida pseudotropicalis. Lactase enzymes are available both in liquid form, e.g., as solutions in water/glycerin, or in powder form. The activity of these enzymes is based on neutral lactase units (NLU) as determined by assay and falls in the range of from approximately 1000 to 5000 NLU/gram. It requires one gallon of 1000 NLU/gram activity product to convert 1000 gallons of milk to a 70% lactose hydrolysis level in twenty-four hours when the milk is stored at 40.degree. F. Conversely, it requires 1/5 of a gallon of 5000 NLU/gram activity product to accomplish 70% lactose hydrolysis in twenty-four hours when the milk is stored at 40.degree. F.
The Food and Drug Administration has determined that hydrolyzed lactose products must contain at least 70% less lactose than the non-hydrolyzed product. Lactose-hydrolyzed, ultra-pasteurized or pasteurized milk containing at least 70% less lactose have been available in the USA for several years.
The literature describes several methods for hydrolyzing the lactose (see R. R. Mahoney, supra). The most widely used process today involves the addition of lactase enzymes and incubation at 40.degree. F. for the necessary time to achieve at least 70% lactose hydrolysis. The major disadvantage of this method is the cost of the enzyme. Another problem associated with this process is the inability to control closely the end point of the hydrolysis. This is because of the time required to inactivate the enzyme in a whole batch of milk in a commercial dairy. To overcome these problems a continuous process using immobilized enzymes was proposed. However, this process is not commercially utilized for the hydrolysis of milk at this time.
Since glucose and galactose, the products of hydrolyzed lactose, are sweeter than lactose, lactose-hydrolyzed milk, when tasted, is sweeter than regular milk. This detracts significantly from its consumer acceptance.
Jacober-Pivarnik et al., Journal of Food Science, 49, 435-438, 445 (1984), disclose an enzyme assay that can be used to accurately reflect lactase activity using a nonfat dry milk substrate. The assay was used to evaluate the effect of potassium ions, incorporated as potassium chloride, as a stabilizer and activator on four yeast lactase enzymes. In the description of the procedure used in studying the effect of potassium ion, it is disclosed that a concentration of 36 mM KCl, i.e., about 0.27% by weight, was used throughout the study since it reflected the level of potassium ions present in milk.